How to Buy Yourself More Elbow Room in Coach More Airlines Now Allow Any Flier to Purchase an Extra Seat; Getting the Space of Business Class for $1,736 Less

Procedures for buying a one-for-two ticket vary: Continental books the extra seat with the passenger’s last name and then uses the first name “Extra Seat” on the second seat; American just has an electronic designation in its computer system that blocks the extra seat from being assigned to someone else; Southwest, when it does sell extra seats, makes the booking in the passenger’s name with XS (“extra seat”) as the middle initials.

Of course, landing an upgrade to business class is usually a better option than buying two coach seats. Frequent fliers on most airlines vie for upgrades using miles, upgrade credits or cash.

But upgrades can be very difficult to secure—and you often don’t know if you have one until shortly before your flight departs.

But, so far, airlines say that the two-seat strategy is little-used.

“Some people have medical needs or just want extra room regardless of their size,” said a spokeswoman for Delta. American says it sometimes sees “professional musicians who purchase a seat for their fragile instruments. There are others, of course, too, but it is fairly uncommon.”

And there is a psychological peril for customers, especially large-sized individuals. Buying two seats can tag you as a “passenger of size” whether you want that or not.

Hollywood director Kevin Smith routinely buys two seats on Southwest. Though he is large and says he has difficulty getting his seat belt buckled, Mr. Smith says he buys the extra seat for comfort and for seclusion.

Regardless of whether he considers a second seat a luxury, Southwest classifies him as a “customer of size.” On Feb. 13, Mr. Smith had two seats reserved for a flight from Oakland to Burbank, Calif., but wanted to hop on an earlier flight. Only one seat was available, and after letting him board, Southwest told him he had to get off the flight.

Southwest’s policy says passengers have to not only be able to get into its 17-inch-wide seats but also not “compromise any portion of adjacent seating.”

Furious, Mr. Smith attacked Southwest in cyberspace and his feud with the airline, which publicly apologized, quickly became national news.

“Southwest Airlines is the Greyhound of the sky,” Mr. Smith said in a podcast about the incident. “I think I can indulge myself with two seats because it is an air bus.”

Several international airlines do offer a compromise between pinched coach and plush business-class—”premium economy” seating that gives coach customers more room at higher ticket prices, but still far cheaper than business-class. Ticket prices generally run 30% to 90% more than coach prices, and you usually get several extra inches of legroom and sometimes other perks like access to premium-level security lines and early boarding.

Air France’s premium economy seats, however, are the same 18-inch width as regular coach seats.

Domestically, United offers “Economy Plus” rows that have five inches of extra legroom, on average. Buying into that may help with room to stretch, snooze or work on a laptop, but it doesn’t spare you from a snoring neighbor bumping your elbows or splaying knees into your space.